The present invention relates to electrical components and methods for making electrical components and in particular to electrical components with leads having selected regions plated with solder and other regions devoid of solder plating. The regions devoid of solder plating contact an encasement material which encases the electrical component so that voids or spaces in the interface between the encasement material and the leads are not formed when the leads are heated during subsequent soldering.
The problem of flux or wash residue contaminants penetrating a case or housing in which an electrical component is encased is well known. Specifically, such wash residues or fluxes penetrate the encasement through small voids in the interface between the leads and the encasement. Such voids or spaces between the leads and the encasement material can be formed during the solder reflow processes such as wave or hand soldering or board washing operations. If not properly removed, flux or washing residues can enter the interior of the electrical device through such interface spaces causing component failure.
For example, in solder ref low processes, amine-activated water soluble fluxes are used followed by reflow soldering and water rinses. This process can cause small openings between the interface between the lead and the encasement material. During the reflow solder process these small openings provide a path to the interior of the electronic component in the encasement material allowing solder residue contamination and ultimate component failure.
While the mechanism that causes the opening of these paths or voids between the leads and the encasement material is not exactly known, one hypothesis is that the path is caused by capillary action during reflow allowing the plating material on the lead to migrate in the direction of the solder wave thereby leaving small openings at the case-to-lead interface. Another hypothesis is that the heat involved in the solder reflow process causes differential expansion of the encasement material-to-lead interface. After the thermal cycle of heating and cooling, small openings may be left at the interface between the lead and the encasement.
Regardless of the cause, any small openings that accumulate residues are detrimental to the normal performance and life of the particular component. It is therefore desired to eliminate openings between the lead-to-encasement interface during the reflow process to thereby minimize the problem of residues being deposited inside the interface between the lead and encasement.